The present invention relates to a feed apparatus, and more particularly, to a sheet paper feed apparatus suited to an image forming apparatus.
FIG. 1 generally shows an image forming apparatus 10 as one example of an apparatus in which a sheet paper feed apparatus of a general type has been incorporated.
Around the periphery of a photosensitive drum 11, are disposed a cleaner 12, a pre-charger 13, an exposer 14, a developer 15, a transfer unit 16 and the like.
The photosensitive drum 11 rotates in the direction indicated by the arrow A and first forms a latent image, and then a toner image.
Numeral 17 represents a flush light fixing apparatus.
Numeral 18 and 19 represent sheet paper feed apparatus.
The sheet paper 20 is supplied from a paper supply portion (not indicated in the figure), is fed in the direction of the arrow B by the feed apparatus 19 and then is conveyed in the direction of the arrow C by the feed apparatus 18, and discharged to the stacker portion (not indicated in the figure).
The transfer unit 16 transfers the toner image on the photosensitive drum 11 to the sheet paper 20 and the toner image on the sheet paper 20 is fixed to the sheet paper 20 by the flush light fixing apparatus 17.
In recent years, the operation of the image forming apparatus 10 has increased and accompanying this has been an increase in the feed speed of sheet paper.
When sheet paper is fed at high speed, it is that much easier for the status of the sheet paper that is being fed, to become unstable, and thus for paper misfeed to occur.
Because of this, it is necessary to improve the feed apparatus 18, 19 so that they have a higher reliability.
FIG. 2 shows conventional sheet feed apparatus 31, 32 and 33 corresponding to the sheet paper feed apparatus represented by the numeral 18 in FIG. 1.
The sheet feed apparatus 31, 32 and 33 are lined up in direction C for feeding the sheet paper.
Each of the sheet feed apparatus 31, 32 and 33 has a structure where hollow fixed center shafts 31-1, 32-1 and 33-1 carry rollers 31-2, 32-2 and 33-2, respectively, so that they are rotatable.
Each of the rollers 31-2, 32-2 and 33-2 has formed along its entire periphery a plurality of holes 31-2a, 32-2a and 33-2a.
In addition, each of the hollow fixed center shafts 31-1, 32-1 and 33-1 has respectively formed in it openings 31-1a, 32-1a and 33-1a.
Each of the hollow fixed center shafts 31-1, 32-1 and 33-1 communicates with a negative pressure source 34.
The rollers 31-2, 32-2 and 33-2 are rotated in the counterclockwise direction as indicated by the arrow D, and of the plurality number of holes 31-2a 32-2a and 33-2a, the holes that successively oppose openings 31-1a, 32-1a and 33-1a produce a suction action that causes the sheet paper to adhere to them while the rotational force of the rollers 32-2 through 33-2 applies a feed force in the direction of the arrow C.
The sheet paper 20 is adhered by the portions of each of the apparatus 31, 32 and 33 and is thereby fed.
Here, the openings 31-1a, 32-1a and 33-1a are formed at portions that are inclined by the angle .alpha.=10.degree.) in the direction opposite the sheet paper feed direction (clockwise, in FIG. 2) with respect to the surfaces 35, 36 and 37 that are vertical with respect to the sheet paper feed surface 22 which passes through the centers of the apparatus 31, 32 and 33. This structure is adopted so as to adhere, as soon as possible, the sheet paper that has been fed and arrived.
As is shown in the enlarged view of FIG. 3, each of the plurality of holes 33-2a perform suction action while it moves from a position on the forward side with respect to the topmost point of the apparatus 33 to the topmost portion. The sheet paper 1 is thereby applied a feed force F1, as indicated by the arrow, in a direction inclining upwards by the angle .alpha. with respect to the sheet feed surface 22.
Because of this, as shown in FIG. 2, the sheet paper 20 rises up from the sheet feed surface 22 and the distal end of the sheet paper 20 catches on the step portion 24 of the lower surface of the flush light fixing apparatus 17 and causes paper misfeed.
FIG. 4 shows a conventional sheet paper feed apparatus 41, corresponding to the sheet paper feed apparatus represented by the number 19 in FIG. 1.
The sheet paper feed apparatus 41 is provided with a negative pressure source 44 passing through a hollow member 42 which is provided with a rotatable roller 43, and is disposed so as to be opposite and in the vicinity of the photosensitive drum 11.
Along the entire periphery of the roller 43 are formed a plurality of holes 46.
The hollow member 42 is formed with a single opening 47 that opposes the sheet paper peeling position 48 on the peripheral surface of the photosensitive drum 11.
The roller 43 rotates in the direction indicated by the arrow D, and the holes 46 come to successively oppose the opening 47 so that the holes 46 opposing the opening 47 produce a suction action. Accordingly, the sheet paper 20 is adhered to the roller 43 and is peeled from the photosensitive drum 11, at the same time as it is being conveyed in the direction of the arrow B by the rotation of the roller 43.
The holes 46 and the openings 47 have their relationship determined by the length "a" of the wall portion 50 between adjacent holes 46 and by the diameter "b" of the opening 47, where a&gt;b.
Because of this, between the time when one of the holes 46 has passed the portion of the opening 47, and the next hole 46 is about to oppose the opening 47, the wall portion 50 completely covers the opening 47. At times such as this, the apparatus 41 does not generate a suction peeling force and resulting in no feed force.
For example, when the portion of the holes 46-1 through 46-3 rotates over the position of the opening 47, the holes 46-1 through 46-3 apply a suction force as indicated by the lines 51, 52 and 53 in FIG. 5 (A) through (C), and the suction force is intermittently applied in the sectional portion as indicated by the line 54 in FIG. 5 (D).
In addition, each of the holes 46-1 through 46-3 applies a feed force as shown by the lines 55, 56 and 57 in FIG. 6 (A) through (C), and the application of the feed force is intermittently in phase as shown by line 58 in FIG. 6 (D).
Because of this intermittent action when the photosensitive drum 11 in particular, is rotating at high speed and feeding the sheet paper 20 at high speed, there is the likelihood that the feeding of the sheet paper 20 will become unstable.